Flexible display device with touch panel

ABSTRACT

A flexible display device includes a display panel including a first surface including a display area configured to display an image, and a second surface disposed on the opposite side of the display panel from the first surface, and a touch panel disposed on the first surface, the touch panel including a base film and a transparent conductive layer disposed on a surface of the base film facing the display panel, in which at least a portion of each of the display panel and the touch panel is bendable such that centers of curvature of the display panel and the touch panel are positioned outside the second surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from and the benefit of Korean PatentApplication No. 10-2014-0088639, filed on Jul. 14, 2014, which is herebyincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND

1. Field

Exemplary embodiments of the inventive concept relate to a flexibledisplay device, and more particularly, to a flexible display deviceincluding a capacitive type external touch panel.

2. Discussion of the Background

A touch panel disposed on a display device provides a touch sensingfunction that facilitates interaction with a user. The touch sensingfunction extracts contact information, such as sensing a touch orlocation of a touched surface when a user approaches or contacts thesurface of the display device with the user's finger or a touch pen. Thedisplay device may receive image signals based on the contactinformation to display corresponding images.

The capacitive touch panel may include a sensing capacitor havingsensing electrodes. The capacitive touch panel may determine whether atouch was made and a location of a touched surface by sensing a changein electrostatic capacitance of the sensing capacitor that is generatedwhen a conductor, such as a finger of the user, approaches the touchpanel. The sensing electrodes may be formed of a transparent conductivelayer such as indium tin oxide (ITO), and patterned on a transparentsubstrate.

The development of the flexible display device requires providingflexibility to the touch panel. Accordingly, a touch panel including asubstrate formed of a transparent plastic film has been developed.However, transparent conductive layer used as the sensing electrodes mayhave high light transmittance and high electrical conductivity but lowflexibility. In other words, while transparent conductive layer may bethin, it may maintain a brittle characteristic.

Silver nanowire (AgNW), carbon nanotubes (CNT), or graphene may beconsidered as an electrode material for replacing the transparentconductive layer of the touch panel, but these materials may have a lowoptical characteristic (low light transmittance). Meanwhile, a techniqueof pre-forming a curved substrate of the touch panel and then adheringthe sensing electrode to the curved surface of the substrate may also beconsidered. However, it may be difficult to pattern the sensingelectrode to the curved surface of the substrate.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the inventive concept,and, therefore, it may contain information that does not form the priorart that is already known in this country to a person of ordinary skillin the art.

SUMMARY

Exemplary embodiments of the inventive concept provide a flexibledisplay device capable of suppressing cracks in a transparent conductivelayer caused by bending when the transparent conductive layer, such asindium tin oxide (ITO), is employed as a sensing electrode of a touchpanel.

Exemplary embodiment of the inventive concept also provide a flexibledisplay device capable of having a specific curved shape or ofrepetitive folding and including a touch panel manufactured bypatterning sensing electrodes on a flat substrate.

Additional aspects of the inventive concept will be set forth in thedetailed description which follows, and, in part, will be apparent fromthe disclosure, or may be learned by practice of the inventive concept.

An exemplary embodiment of the inventive concept provides a flexibledisplay device includes a display panel including a first surfaceincluding a display area configured to display an image, and a secondsurface disposed on the opposite side of the display panel from thefirst surface; and a touch panel disposed on the first surface, thetouch panel including a base film and a transparent conductive layerdisposed on a surface of the base film facing the display panel, inwhich at least a portion of each of the display panel and the touchpanel is bendable such that centers of curvature of the display paneland the touch panel are positioned outside the second surface.

The transparent conductive layer may further include a sensing electrodedisposed on the base film and a functional coating layer covering thetransparent conductive layer and the sensing electrode unit, in whichthe functional coating layer may be configured to create an anchoreffect with the sensing electrode unit.

The functional coating layer may contain an acryl-based resin or apolyurethane-based resin, and the thickness of the functional coatinglayer is in a range from 0.1 μm to 30 μm.

The functional coating layer may have a refractive index in a range from1.3 to 2.0.

The functional coating layer may be covered with a protective film. Theprotective film may contain at least one of polyethylene terephthalate(PET), a cyclo-olefin polymer (COP), triacetyl cellulose (TAC), and apolycarbonate (PC).

Another exemplary embodiment of the inventive concept provides aflexible display device includes a display panel including a firstsurface including a display area configured to display an image, and asecond surface disposed on the opposite side to the display panel fromthe first surface, and a touch panel disposed on the first surface, thetouch panel including a base film and a sensing electrode unit includinga transparent conductive layer disposed on the base film, in which thesensing electrode unit includes first sensing electrodes extending in afirst direction and second sensing electrodes disposed in a seconddirection perpendicular to the first direction, at least one of thefirst sensing electrodes and the second sensing electrodes is disposedon a surface of the base film facing the display panel, and at least aportion of each of the display panel and the touch panel is bendablesuch that centers of curvature of the display panel and the touch panelare positioned outside the second surface.

The first sensing electrodes and the second sensing electrodes may bedisposed on a surface of the base film facing the display panel, and thefirst sensing electrodes may be insulated from the second sensingelectrodes by an insulating layer.

The first sensing electrodes and the second sensing electrodes may becovered with a functional coating layer, and the functional coatinglayer may be covered with a protective film.

The touch panel may include a first base film and a second base filmoverlapping each other, the first sensing electrodes may be disposed ona surface of the first base film facing the display panel, and thesecond sensing electrodes may be disposed on a surface of the secondbase film facing the display panel.

The first sensing electrodes may be covered with a first functionalcoating layer, and the second sensing electrodes may be covered with asecond functional coating layer.

The second functional coating layer may be disposed closer to thedisplay panel than the first functional coating layer, and the secondfunctional coating layer may be covered with a protective film.

The touch panel may include a first base film and a second base filmoverlapping each other, and the first sensing electrodes may be disposedon a surface of the first base film facing the display panel. The secondbase film may be disposed closer to the display panel than the firstbase film, and the second sensing electrodes may be disposed on asurface of the second base film facing the first base film.

The first sensing electrodes may be covered with a first functionalcoating layer, and the second sensing electrodes may be covered with asecond functional coating layer.

Yet another exemplary embodiment of the inventive concept provides aflexible display device includes a display panel including a firstsurface including a display area configured to display an image, and asecond surface disposed on the opposite side of the display panel fromthe first surface, a touch panel disposed on the first surface, thetouch panel including a base film and a sensing electrode unit includinga transparent conductive layer, and a cover window disposed on the touchpanel, in which the sensing electrode unit includes first sensingelectrodes disposed on a surface of the cover window facing the basefilm, and second sensing electrodes disposed on a surface of the basefilm facing the display panel, and at least a portion of each of thedisplay panel, the touch panel, and the cover window is bendable, suchthat centers of curvature thereof are positioned outside the secondsurface.

The first sensing electrodes may be covered with a first functionalcoating layer, and the second sensing electrodes may be covered with asecond functional coating layer. The second functional coating layer maybe covered with a protective film.

According to exemplary embodiments of the inventive concept, a stressapplied to a transparent conductive layer of a touch panel may bereduced, thereby suppressing crack generation of the transparentconductive layer and improving folding endurance. Further, the touchpanel according to the exemplary embodiments may require no changes inthe existing manufacturing process and electrode materials of the touchpanel, and thus may be easily manufactured by using the same process.

The foregoing general description and the following detailed descriptionare exemplary and explanatory and are intended to provide furtherexplanation of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the inventive concept, and are incorporated in andconstitute a part of this specification, illustrate exemplaryembodiments of the inventive concept, and, together with thedescription, serve to explain principles of the inventive concept.

FIG. 1 is a schematic cross-sectional view illustrating a flexibledisplay device according to an exemplary embodiment of the inventiveconcept.

FIG. 2, FIG. 3, and FIG. 4 are respectively schematic cross-sectionalviews of variations of the flexible display device shown in FIG. 1.

FIG. 5 is a block diagram illustrating a display panel and a touch panelof the flexible display device shown in FIG. 1.

FIG. 6 is a bottom view illustrating a touch panel of the flexibledisplay device shown in FIG. 1.

FIG. 7 is a partially enlarged view of FIG. 6.

FIG. 8 is a cross-sectional view taken along the line II-II of FIG. 6.

FIG. 9 is a schematic diagram illustrating a touch panel of the flexibledisplay device of FIG. 1.

FIG. 10 is a schematic diagram illustrating a touch panel according to acomparative embodiment.

FIG. 11 is a graph illustrating threshold strains according to a tensileforce and a compressive force of a transparent conductive layer.

FIG. 12 is a graph illustrating stresses according to a radius ofcurvature of the transparent conductive layer.

FIG. 13 is a cross-sectional view of a touch panel of a flexible displaydevice according to an exemplary embodiment of the inventive concept.

FIG. 14 is a cross-sectional view of a touch panel of a flexible displaydevice according to an exemplary embodiment of the inventive concept.

FIG. 15 is a cross-sectional view of a touch panel of a flexible displaydevice according to an exemplary embodiment of the inventive concept.

FIG. 16 is a cross-sectional view of a touch panel of a flexible displaydevice according to an exemplary embodiment of the inventive concept.

FIG. 17 is a cross-sectional view of a touch panel of a flexible displaydevice according to an exemplary embodiment of the inventive concept.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of various exemplary embodiments. It is apparent, however,that various exemplary embodiments may be practiced without thesespecific details or with one or more equivalent arrangements. In otherinstances, well-known structures and devices are shown in block diagramform in order to avoid unnecessarily obscuring various exemplaryembodiments.

In the accompanying figures, the size and relative sizes of layers,films, panels, regions, etc., may be exaggerated for clarity anddescriptive purposes. Also, like reference numerals denote likeelements.

When an element or layer is referred to as being “on,” “connected to,”or “coupled to” another element or layer, it may be directly on,connected to, or coupled to the other element or layer or interveningelements or layers may be present. When, however, an element or layer isreferred to as being “directly on,” “directly connected to,” or“directly coupled to” another element or layer, there are no interveningelements or layers present. For the purposes of this disclosure, “atleast one of X, Y, and Z” and “at least one selected from the groupconsisting of X, Y, and Z” may be construed as X only, Y only, Z only,or any combination of two or more of X, Y, and Z, such as, for instance,XYZ, XYY, YZ, and ZZ. Like numbers refer to like elements throughout. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

Although the terms first, second, etc. may be used herein to describevarious elements, components, regions, layers, and/or sections, theseelements, components, regions, layers, and/or sections should not belimited by these terms. These terms are used to distinguish one element,component, region, layer, and/or section from another element,component, region, layer, and/or section. Thus, a first element,component, region, layer, and/or section discussed below could be termeda second element, component, region, layer, and/or section withoutdeparting from the teachings of the present disclosure.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, may be used herein for descriptive purposes, and,thereby, to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the drawings. Spatiallyrelative terms are intended to encompass different orientations of anapparatus in use, operation, and/or manufacture in addition to theorientation depicted in the drawings. For example, if the apparatus inthe drawings is turned over, elements described as “below” or “beneath”other elements or features would then be oriented “above” the otherelements or features. Thus, the exemplary term “below” can encompassboth an orientation of above and below. Furthermore, the apparatus maybe otherwise oriented (e.g., rotated 90 degrees or at otherorientations), and, as such, the spatially relative descriptors usedherein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting. As used herein, thesingular forms, “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. Moreover,the terms “comprises,” comprising,” “includes,” and/or “including,” whenused in this specification, specify the presence of stated features,integers, steps, operations, elements, components, and/or groupsthereof, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof.

Various exemplary embodiments are described herein with reference tosectional illustrations that are schematic illustrations of idealizedexemplary embodiments and/or intermediate structures. As such,variations from the shapes of the illustrations as a result, forexample, of manufacturing techniques and/or tolerances, are to beexpected. Thus, exemplary embodiments disclosed herein should not beconstrued as limited to the particular illustrated shapes of regions,but are to include deviations in shapes that result from, for instance,manufacturing. For example, an implanted region illustrated as arectangle will, typically, have rounded or curved features and/or agradient of implant concentration at its edges rather than a binarychange from implanted to non-implanted region. Likewise, a buried regionformed by implantation may result in some implantation in the regionbetween the buried region and the surface through which the implantationtakes place. Thus, the regions illustrated in the drawings are schematicin nature and their shapes are not intended to illustrate the actualshape of a region of a device and are not intended to be limiting.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure is a part. Terms,such as those defined in commonly used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of the relevant art and will not be interpreted in anidealized or overly formal sense, unless expressly so defined herein.

FIG. 1 is a schematic cross-sectional view illustrating a flexibledisplay device 100 according to an exemplary embodiment of the inventiveconcept.

Referring to FIG. 1, the flexible display device 100 according to thefirst exemplary embodiment includes a display panel 10 and a touch panel20 disposed on the display panel 10. The display panel 10 includes afirst surface 11 on which a display area (DA in FIG. 5) is formed, and asecond surface 12 disposed on the opposite side of the display panel 10from the first surface. The touch panel 20 is disposed on the firstsurface 11 to cover the display area.

The flexible display device 100 may further include a polarizationmember 30 disposed between the display panel 10 and the touch panel 20,and a cover window 40 that is disposed on the touch panel 20. Thepolarization member 30 may be formed of a combination of a linearpolarizer and a quarter wave plate, and may suppress reflection ofexternal light. The touch panel 20 may be adhered on the polarizationmember 30 by a first transparent adhesive layer 51, and the cover window40 may be attached on the touch panel 20 by a second transparentadhesive layer 52.

Each of the display panel 10, the polarization member 30, the touchpanel 20, and the cover window 40 may be formed of a flexible plasticfilm as a basic member, thereby having a flexible characteristic ofbeing bendable by an external force. In FIG. 1, the flexible displaydevice 100 is illustrated as having a stacked structure of the displaypanel 10, the polarization member 30, the touch panel 20, and the coverwindow 40. However, the positions of the polarization member 30 and thetouch panel 20 may be switched.

The flexible display device 100 is formed to have a single curvature ona whole part thereof, thereby being bendable. In this case, a center ofthe curvature is positioned outside the second surface 12 of the displaypanel 10. That is, the center of the curvature is the end point of aradius line extending from the curved display panel 10. As a result, ascreen of the flexible display device 100 is convexly bendable withrespect to a user. The flexible display device 100 may staticallymaintain a bended state, or may repeatedly accomplish the bended stateand a flat state. In the case of repeatedly accomplishing the bendedstate and the flat state, the flexible display device 100 may bedescribed to have a foldable or bendable function.

The flexible display device 100 may have various curved shapes includingthe curved shape shown in FIG. 1. FIG. 2 to FIG. 4 are schematiccross-sectional views of various exemplary variations of the flexibledisplay device 100 shown in FIG. 1. For the convenience of description,in FIG. 2 to FIG. 4, each of the flexible display devices 110, 120, and130 is briefly illustrated with the display panel 10, the polarizationmember 30, the touch panel 20, and the cover window 40.

Referring to FIG. 2, a flexible display device 110 according to anexemplary embodiment includes a flat portion FA, and a first curvedportion CA1 and a second curved portion CA2 that are respectivelydisposed at opposite sides of the flat portion FA. Centers of thecurvature of the first curved portion CA1 and the second curved portionCA2 are positioned outside the second surface 12 of the display panel10. A radius of curvature of the first curved portion CA1 may be set tobe the same as or different from that of the second curved portion CA2.

Referring to FIG. 3, a flexible display device 120 according to anotherexemplary embodiment includes a curved portion CA, and a first flatportion FA1 and a second flat portion FA2 that are respectively disposedat opposite sides of the curved portion CA. A center of the curvature ofthe curved portion CA is positioned outside the second surface 12 of thedisplay panel 10. A width of the first flat portion FA1 may be set to bethe same as or different from that of the second flat portion FA2.

Referring to FIG. 4, a flexible display device 130 according to anotherexemplary embodiment is bended in such a ring shape so as to foldopposite ends thereof around each other or to overlap their parts witheach other. In this case, centers of the curvature are positionedoutside the second surface 12. In all of the exemplary embodiments shownin FIG. 1 to FIG. 4, the flexible display devices 100, 110, 120, and 130may statically maintain a bended state, or may repeatedly accomplish thebended state and a flat state.

Various curved shapes that can be embodied by the flexible displaydevice are illustrated in FIG. 1 to FIG. 4, but the curved shape of theflexible display device is not limited thereto. In all of the exemplaryembodiments shown in FIG. 1 to FIG. 4, at least a part of each of theflexible display devices 100, 110, 120, and 130 is bendable, and thecenters of their curvature are positioned outside the second surface 12.

FIG. 5 is a block diagram illustrating a display panel 10 and a touchpanel 20 of the flexible display device 100 shown in FIG. 1.

Referring to FIG. 5, a display area DA on which an image may bedisplayed is disposed on the first surface 11 of the display panel 10.The display panel 10 may be a flat display panel such as an organiclight emitting diode (OLED) device, a liquid crystal display (LCD), oran electrophoretic display device. By employing a plastic film such aspolyimide as a substrate, the display panel 10 may have a flexiblecharacteristic of being bendable by an external force.

In the display area DA, a plurality of pixels PX, a plurality of gatelines (not shown) connected to the pixels PX to transmit drivingsignals, and a plurality of data lines (not shown) may be disposed. Inthe case of the organic light emitting diode panel, each pixel PX mayinclude a gate line, a switching element (not shown) connected to thedata line, and a pixel electrode (not shown) connected to the switchingelement.

The switching element may be turned on or off according to a gate signalfrom the gate line to selectively transmit a data signal from the dataline to a pixel electrode. The pixel PX may further include a commonelectrode (not shown) disposed to be opposite to the pixel electrode andan emission layer disposed between the pixel electrode and the commonelectrode to form a light-emitting device. The gate line and the dataline may be extended to a peripheral area PA1 to form a pad portion (notshown).

A display controller 61 may receive an input signal containing luminanceinformation of each pixel PX and an input control signal for controllingdisplay thereof from an external device. The display controller 61 mayconvert the input image signal into an output image signal by processingit based on the input control signal, and may generate control signalssuch as a gate control signal and a data control signal. The displaycontroller 61 may output a gate control signal to a gate driver (notshown), and a data control signal and an output image signal to a datadriver (not shown).

The touch panel 20 includes a touch region TA that includes a sensingelectrode unit 22 and a peripheral area PA2 positioned outside the touchregion TA. At the peripheral area PA2, connection wires (not shown) forconnecting each of first sensing electrodes 23 and second sensingelectrodes 24 to a touch controller 62 may be formed.

The touch region TA may sense a touch when an object actually approachesor contacts the flexible display device 100. Herein, the contact mayinclude an external object, such as a user's finger, approaching theflexible display device 100, hovering while the external objectapproached the flexible display device 100, or directly contacting theflexible display device 100. The touch region TA may be formed to havean area that is equal to or smaller than that of the display area DA.

The touch controller 62 may be connected to the sensing electrode unit22 to control an operation of the touch panel 20. The touch controller62 may transmit a sensing input signal to the sensing electrode unit 22or may receive a sensing output signal to perform processing. The touchcontroller 62 may process the sensing output signal to generate contactinformation which may include whether a touch was made and a location ofthe touched surface of the flexible display device 100. The touch panel20 may be connected to the touch controller 62 and the displaycontroller 61 so that the operation thereof may be controlled.

FIG. 6 is a bottom view illustrating a touch panel 20 of the flexibledisplay device 100 shown in FIG. 1. FIG. 7 is a partially enlarged viewof FIG. 6, and FIG. 8 is a cross-sectional view taken along the lineII-II of FIG. 6. For convenience of description, in FIG. 6 to FIG. 8,the touch panel is illustrated as a flat type.

Referring to FIG. 6 to FIG. 8, the touch panel 20 according to thepresent exemplary embodiment includes a transparent base film 21, and asensing electrode unit 22 disposed on a surface of the base film 21facing the display panel 10. The base film 21 may be formed of a polymerfilm such as polyimide to provide flexibility to the touch panel 20.

The sensing electrode unit 22 may include a plurality of first sensingelectrodes 23 arranged in a first direction, and a plurality of secondsensing electrodes 24 arranged in a second direction while maintainingan insulating state from the first sensing electrodes 23. Herein, thefirst direction and the second direction may be perpendicular to eachother, thereby the first sensing electrodes 23 and the second sensingelectrodes 24 are arranged in a matrix form.

The first sensing electrodes 23 may include a plurality of first sensingcells 231, and a plurality of first connections 232 for connecting thefirst sensing cells 231. The second sensing electrodes 24 may include aplurality of second sensing cells 241, and a plurality of secondconnections 242 for connecting the second sensing cells 241. Each of thesensing cells 231 and 241 has a quadrangular shape. The first sensingcells 231 and the second sensing cells 241 are separated from each otherto prevent them from being folded by or overlap with each other. Thefirst connections 232 and the second connections 242 overlap with eachother, but an insulating layer 25 may be disposed therebetween toprevent electrical connection.

According to the present exemplary embodiment, the sensing electrodeunit 22 may be formed of a transparent conductive layer. The transparentconductive layer may include at least one of indium tin oxide (ITO),indium zinc oxide (IZO), indium oxide (In₂O₃), and zinc oxide (ZnO).

At the peripheral area PA2 positioned outside the touch region TA,connection wires 26 for connecting each of the first sensing electrodes23 and the second sensing electrodes 24 to the touch controller 62 areformed. The connection wires 26 may be formed of a low-resistance metalfilm such as molybdenum (Mo), silver (Ag), titanium (Ti), cooper (Cu),and aluminum (Al), as well as a transparent conductive layer.

The touch controller 62 may sense a touch position by inputting asensing input signal into at least one of the first sensing electrodes23 and the second sensing electrodes 24 and receiving a sensing outputsignal. A method for sensing the touch position may include aself-capacitance method and a mutual capacitance method. For example, inthe self-capacitance method, the first sensing electrodes 23 and thesecond sensing electrodes 24 receive the sensing input signal. When aconductive object such as a finger or a touch pen contacts a specificregion of the touch region TA, the capacitance of the sensing electrodeunit 22 in that region may change. Then, the touch controller 62searches for a position of the first sensing electrodes 23 or the secondsensing electrodes 24 in which the capacitance change is sensed, anddetects it as the touch position.

The touch panel 20 may prevent crack generation caused by bending bychanging the position of the sensing electrode unit 22 while employingthe transparent conductive layer, such as ITO, as the sensing electrodeunit 22. Specifically, the sensing electrode unit 22 is formed on asurface of the base film 21 facing the display panel 10, rather thanbeing formed on a surface of the base film 21 facing the cover window40. In this case, at least a part of the flexible display device 100,and a center of the curvature thereof, is positioned outside the secondsurface 12 of the display panel 10.

FIG. 9 is a schematic diagram illustrating a touch panel 20 of theflexible display device 100 of FIG. 1. FIG. 10 is a schematic diagramillustrating a touch panel 201 according to a comparative embodiment.

As shown in FIG. 9, in the touch panel 20 according to the presentexemplary embodiment, a transparent conductive layer 27 is formed on asurface of the base film 21 facing a center of the curvature thereof. Incontrast, as shown in FIG. 10, in a touch panel 201 according to acomparative embodiment, a transparent conductive layer 271 may be formedon a surface of the base film 21 that is opposite to a center of thecurvature thereof. As a result, a compressive force is applied to thetransparent conductive layer 27 according to the present exemplaryembodiment, while a tensile force is applied to the transparentconductive layer 271 according to the comparative embodiment.

FIG. 11 is a graph illustrating threshold strains according to a tensileforce and a compressive force of a transparent conductive layer 27 and271.

As shown in FIG. 11, a threshold strain (1.1%) of the transparentconductive layer 271 to which the tensile force is applied is smallerthan a threshold strain (1.7%) of the transparent conductive layer 27 towhich the compressive force is applied in two transparent conductivelayers having the same size and thickness. Accordingly, the transparentconductive layer 27 to which the compressive force is applied isstronger than the transparent conductive layer 271 to which the tensileforce is applied, with respect to an external force.

FIG. 12 is a graph illustrating stresses according to a radius ofcurvature of the transparent conductive layer 271. Herein, both of thetouch panels 20 and 201 according to the present exemplary embodimentand the comparative embodiment include a base film 21 having a thicknessof 80 μm.

As shown in FIG. 12, a smaller stress is applied to the transparentconductive layer 27 included in the touch panel 20 according to thepresent exemplary embodiment than in the touch panel 201 according tothe comparative embodiment, under all conditions of the radius ofcurvature in a range of 4 mm to 6 mm. Specifically, under the conditionof the radius of curvature of 5 mm, the stress of the transparentconductive layer 27 included in the touch panel 20 according to thepresent exemplary embodiment is smaller than that of the transparentconductive layer 271 included in the touch panel 201 according to thecomparative embodiment.

As such, the touch panel 20 according to the present exemplaryembodiment can more efficiently suppress crack generation of thetransparent conductive layer 27 thereof by reducing the stress of thetransparent conductive layer 27 than the touch panel 201 according tothe comparative embodiment, thereby improving folding endurance.Accordingly, the flexible display device 100 may improve durability ofthe product by suppressing failure occurrence of the touch panel 20caused by folding.

The touch panel 20 according to the present exemplary embodiment mayrequire no change in the existing manufacturing process and electrodematerials of the touch panel 20, and thus may be easily manufactured byusing the existing manufacturing process. Further, the flat base film 21of the touch panel 20 according to the present exemplary embodiment maybe patterned with the sensing electrode unit 22 and the connection wires26 as in the existing process, and may be easily attached on the displaypanel 10 by using the first transparent adhesive layer 51.

FIG. 13 is a cross-sectional view of a touch panel 210 of a flexibledisplay device according to an exemplary embodiment of the inventiveconcept. All constituent elements other than the touch panel 210 in theflexible display device according to the present exemplary embodimentare substantially similar to those in the flexible display deviceaccording to the exemplary embodiment described with respect to FIG. 1,and repeated description thereof is omitted.

Referring to FIG. 13, the touch panel 210 according to the presentexemplary embodiment may further include a functional coating layer 28that covers the sensing electrode unit 22. The functional coating layer28 may be formed of an acryl-based resin or a polyurethane-based resin.An anchor effect creates a high surface bonding force between thefunctional coating layer 28 and a surface of the sensing electrode unit22, thereby suppressing crack generation. The anchor effect ismechanical bonding that occurs when the functional coating layer 28penetrates to an empty hole or a concave region of the surface of thesensing electrode unit 22 and consolidates therein.

The functional coating layer 28 may be formed by employing a wet-coatingmethod using a liquid resin, or by stacking a dry film resin on thesensing electrode unit 22 and hardening the stacked resin. Thefunctional coating layer 28 may be formed to have a thin thickness in arange from about 0.1 to 30 μm, thereby minimizing an increase in thethickness of the touch panel 210 and a decrease in optical transparency.The functional coating layer 28 may be formed on the touch region TAonly, or may be formed on the touch region TA and the peripheral areaPA2.

In a typical touch panel, the base film 21 may include an optical indexmatching layer for preventing the sensing electrode unit 22 from beingseen. For example, when the sensing electrode unit 22 is formed of ITO,the base film 21 may include the optical index matching layer includingsilicon dioxide (SiO₂) on a surface thereof facing the sensing electrodeunit 22.

In the present exemplary embodiment, the touch panel 210 can use thefunctional coating layer 28 as the optical index matching layer bycontrolling a refractive index of the functional coating layer 28, andthus the conventional optical index matching layer may be omitted. Thefunctional coating layer 28 may have a refractive index in a range from1.3 to 2.0. When the functional coating layer 28 with a refractive indexwithin the range from 1.3 to 2.0 is formed to have a thickness in arange from 0.1 μm to 30 μm, and the sensing electrode unit 22 is formedof ITO to have a thickness in a range from 10 nm to 200 nm, the sensingelectrode unit 22 may be prevented from being seen.

FIG. 14 is a cross-sectional view of a touch panel 220 of a flexibledisplay device according to an exemplary embodiment of the inventiveconcept. All constituent elements other than the touch panel 220 in theflexible display device according to the present exemplary embodimentare substantially similar to those in the flexible display deviceaccording to the exemplary embodiment described with respect to FIG. 1,and repeated description thereof is omitted.

Referring to FIG. 14, the touch panel 220 according to the presentexemplary embodiment further includes a functional coating layer 28 thatcovers the sensing electrode unit 22, and a protective film 29 thatcovers the functional coating layer 28. The functional coating layer 28according to the present exemplary embodiment is substantially similarto that of the exemplary embodiment described above with respect to FIG.13.

The protective film 29 may block transmission of moisture and chemicalmaterials, and may contain polyethylene terephthalate (PET), acyclo-olefin polymer (COP), triacetyl cellulose (TAC), or apolycarbonate (PC). The protective film 29 protects the sensingelectrode unit 22 and the functional coating layer 28, therebyincreasing chemical resistance and anti-invasion of the touch panel 220.A transparent adhesive layer (not shown) may be interposed between thefunctional coating layer 28 and the protective film 29.

In the flexible display device according to the exemplary embodiments ofthe inventive concept, the first sensing electrodes 23 and the secondsensing electrodes 24 constituting the sensing electrode unit 22 areformed on the same surface. However, the first sensing electrodes 23 andthe second sensing electrodes 24 may be formed on different surfaces.This configuration will be described with reference to FIG. 15 to FIG.17.

FIG. 15 is a cross-sectional view of a touch panel 20 of a flexibledisplay device 400 according to an exemplary embodiment of the inventiveconcept. The same elements will be designated by the same referencenumerals as those in the other exemplary embodiments.

Referring to FIG. 15, in the flexible display device 400 according tothe present exemplary embodiment, the first sensing electrodes 23 areformed on a surface of the cover window 40 facing the touch panel 20,and the second sensing electrodes 24 are formed on a surface of the basefilm 21 facing the display panel 10. The positions of the first sensingelectrodes 23 and second sensing electrodes 24 may be switched.Specifically, the second sensing electrodes 24 may be formed on thecover window 40, and the first sensing electrodes 23 may be formed onthe base film 21.

Since the first sensing electrodes 23 and the second sensing electrodes24 are formed on the different surfaces, no insulating layer forinsulating the first sensing electrodes 23 and the second sensingelectrodes 24 may be provided. The first sensing electrodes 23 formed onthe cover window 40 may be covered with a first functional coating layer281, and the second sensing electrodes 24 formed on the base film 21 maybe covered with a second functional coating layer 282. The materials,thicknesses, and refractive indexes of the functional coating layers 281and 282 are substantially similar to those in the exemplary embodimentdescribed above, and repeated description thereof is omitted.

The second functional coating layer 282 may be covered with theprotective film 29, and the first functional coating layer 281 may alsobe covered with a protective film (not shown). The material and functionof the protective film 29 are substantially similar to those in theexemplary embodiment described above, and repeated description thereofis omitted.

FIG. 16 is a cross-sectional view of a touch panel 20 of a flexibledisplay device 500 according to an exemplary embodiment of the inventiveconcept. The same elements will be designated by the same referencenumerals as those in the exemplary embodiment described above withrespect to FIG. 14.

Referring to FIG. 16, in the flexible display device 500 according tothe present exemplary embodiment, the touch panel 20 includes a firstbase film 211 and a second base film 212 which overlap each other. Thefirst sensing electrodes 23 may be formed on a surface of the first basefilm 211 facing the display panel 10, and the second sensing electrodes24 may be formed on a surface of the second base film 212 facing thedisplay panel 10.

The first sensing electrodes 23 may be covered with the first functionalcoating layer 281, and the second sensing electrodes 24 may be coveredwith the second functional coating layer 282. The materials,thicknesses, and refractive indices of the functional coating layers 281and 282 are substantially similar to those described above with respectto FIG. 13, and repeated description thereof is omitted. The secondfunctional coating layer 282 may be covered with the protective film 29.The material and function of the protective film 29 are substantiallysimilar to those described above with respect to FIG. 14, and repeateddescription thereof is omitted.

FIG. 17 is a cross-sectional view of a touch panel 20 of a flexibledisplay device 600 according to an exemplary embodiment of the inventiveconcept. The same elements will be designated by the same referencenumerals as those described above.

Referring to FIG. 17, in the flexible display device 600 according tothe present exemplary embodiment, the touch panel 20 includes a firstbase film 211 and a second base film 212 which overlap each other. Thefirst sensing electrodes 23 may be formed on a surface of the first basefilm 211 facing the display panel 10, and the second sensing electrodes24 may be formed on a surface of the second base film 212 facing thecover window 40.

The first sensing electrodes 23 may be covered with the first functionalcoating layer 281, and the second sensing electrodes 24 may be coveredwith the second functional coating layer 282. An adhesive layer (notshown) may be disposed between the first functional coating layer 281and the second functional coating layer 282. The materials, thicknesses,and refractive indices of the functional coating layers 281 and 282 aresubstantially similar to those described with respect to FIG. 13, andrepeated description thereof is omitted.

For convenience of description, in FIG. 15 to FIG. 17, the illustrationof the first transparent adhesive layer for adhering the polarizationmember 30 and the touch panel 20 is omitted.

As described above, at least a part of the flexible display device isbendable. Accordingly, the center of the curvature thereof is positionedoutside the second surface 12 of the display panel 10. In the touchpanel 20, the transparent conductive layer may be formed on a surface ofthe base film 21 facing the display panel 10. The transparent conductivelayer formed on the surface of the base film 21 facing the display panel10 may include the first sensing electrodes 23 and the second sensingelectrodes 24 or at least a part thereof.

When bended, the transparent conductive layer formed on the surface ofthe base film 21 facing the display panel 10 may be exposed to acompressive force rather than a tensile force, thereby reducing thestress and suppressing crack generation. In addition, the crackgeneration on the surface may further be suppressed by a high surfacebonding force between the transparent conductive layer and thefunctional coating layer 28. In the flexible display device, thereliability and durability of products can be improved by suppressingthe functional deterioration of the touch panel 20 caused by the cracksof the transparent conductive layer.

Although certain exemplary embodiments and implementations have beendescribed herein, other embodiments and modifications will be apparentfrom this description. Accordingly, the inventive concept is not limitedto such exemplary embodiments, but rather to the broader scope of thepresented claims and various obvious modifications and equivalentarrangements.

What is claimed is:
 1. A flexible display device, comprising: a displaypanel comprising: a first surface comprising a display area configuredto display an image; and a second surface disposed on the opposite sideof the display panel from the first surface; and a touch panel disposedon the first surface, the touch panel comprising: a base film; and atransparent conductive layer disposed on a surface of the base filmfacing the display panel, wherein at least a portion of each of thedisplay panel and the touch panel is bendable, such that centers ofcurvature of the display panel and the touch panel are positionedoutside the second surface.
 2. The flexible display device of claim 1,further comprising: a sensing electrode unit disposed on the base film;and a functional coating layer covering the transparent conductive layerand the sensing electrode unit, wherein the functional coating layer isconfigured to create an anchor effect with the sensing electrode unit.3. The flexible display device of claim 2, wherein: the functionalcoating layer comprises an acryl-based resin or a polyurethane-basedresin; and the thickness of the functional coating layer is in a rangefrom 0.1 μm to 30 μm.
 4. The flexible display device of claim 3, whereinthe functional coating layer has a refractive index in a range from 1.3to 2.0.
 5. The flexible display device of claim 2, further comprising aprotective film covering the functional coating layer.
 6. The flexibledisplay device of claim 5, wherein the protective film comprises atleast one of polyethylene terephthalate (PET), cyclo-olefin polymer(COP), triacetyl cellulose (TAC), and polycarbonate (PC).
 7. A flexibledisplay device, comprising: a display panel comprising: a first surfacecomprising a display area configured to display an image; and a secondsurface disposed on the opposite side of the display panel from thefirst surface; and a touch panel disposed on the first surface, thetouch panel comprising: a base film; and a sensing electrode unitcomprising a transparent conductive layer disposed on the base film,wherein: the sensing electrode unit comprises first sensing electrodesextending in a first direction and second sensing electrodes disposed ina second direction perpendicular to the first direction; at least one ofthe first sensing electrodes and the second sensing electrodes isdisposed on a surface of the base film facing the display panel; and atleast a portion of each of the display panel and the touch panel isbendable, such that centers of curvature of the display panel and thetouch panel are positioned outside the second surface.
 8. The flexibledisplay device of claim 7, wherein: the first sensing electrodes and thesecond sensing electrodes are disposed on the surface of the base filmfacing the display panel; and the first sensing electrodes are insulatedfrom the second sensing electrodes by an insulating layer.
 9. Theflexible display device of claim 8, further comprising: a functionalcoating layer covering the first sensing electrodes and the secondsensing electrodes; and a protective film covering the functionalcoating layer.
 10. The flexible display device of claim 7, wherein: thetouch panel further comprises a first base film and a second base filmoverlapping each other; the first sensing electrodes are disposed on asurface of the first base film facing the display panel; and the secondsensing electrodes are disposed on a surface of the second base filmfacing the display panel.
 11. The flexible display device of claim 10,further comprising: a first functional coating layer covering the firstsensing electrodes; and a second functional coating layer covering thesecond sensing electrodes.
 12. The flexible display device of claim 11,wherein: the second functional coating layer is disposed closer to thedisplay panel than the first functional coating layer; and the secondfunctional coating layer is covered with a protective film.
 13. Theflexible display device of claim 7, wherein: the touch panel furthercomprises a first base film and a second base film overlapping eachother; and the first sensing electrodes are disposed on a surface of thefirst base film facing the display panel.
 14. The flexible displaydevice of claim 13, wherein: the second base film is disposed closer tothe display panel than the first base film; and the second sensingelectrodes are disposed on a surface of the second base film facing thefirst base film.
 15. The flexible display device of claim 14, furthercomprising: a first functional coating layer covering the first sensingelectrodes; and a second functional coating layer covering the secondsensing electrodes.
 16. A flexible display device, comprising: a displaypanel comprising: a first surface comprising a display area configuredto display an image; and a second surface disposed on the opposite sideof the display panel from the first surface; a touch panel disposed onthe first surface, the touch panel comprising: a base film; and asensing electrode unit comprising a transparent conductive layer; and acover window disposed on the touch panel, wherein: the sensing electrodeunit comprises: first sensing electrodes disposed on a surface of thecover window facing the base film; and second sensing electrodesdisposed on a surface of the base film facing the display panel; and atleast a portion of each of the display panel, the touch panel, and thecover window is bendable, such that centers of curvature thereof arepositioned outside the second surface.
 17. The flexible display deviceof claim 16, further comprising: a first functional coating layercovering the first sensing electrodes; and a second functional coatinglayer covering the second sensing electrodes.
 18. The flexible displaydevice of claim 17, further comprising a protective film covering thesecond functional coating layer.